Molecular recognition in partially folded states of a transporter protein: temperature-dependent specificity of bovine serum albumin.

ABSTRACT

The specificity of molecular recognition of a transporter protein bovine serum albumin (BSA) in its different partially folded states has been studied. In order to avoid complications due to chemical denaturation, we have prepared thermally induced partially folded states of the protein. The partially folded states have been structurally characterized by circular dichroism and differential thermal analysis techniques. The change in the globular structure of the protein as a consequence of thermal unfolding has also been characterized by dynamic light scattering. Steady state, picosecond-resolved fluorescence and polarization gated spectroscopies on the ligands (DCM, LDS 750) in the protein reveal the dynamics of the binding sites and the specificity of ligand binding of BSA. Picosecond resolved Förster resonance energy transfer studies on the donor DCM and acceptor LDS 750 confirm that the specificity of ligand binding in the binding site is maintained up to 70 degrees C. At 75 degrees C, the protein loses its specificity of recognition at the aforesaid site.